The invention concerns a seat comprising a seat squab and a backrest which is adjustable in respect of its inclination.
Such a seat involves for example a vehicle seat for a land vehicle, aircraft or marine craft, or a chair such as an office chair or the like.
Hitherto it was assumed that, when a person is sitting, the person should adopt an upright position with a hollow back (lordosis). A large number of proposals have been put forward in that respect. By way of example WO 95/22307 describes a seat having a backrest, wherein lordosis can be adjusted and displaced as desired.
A seat which is adjustable in respect of lordosis, in particular a vehicle seat, is also known for example from DE 195 34 660 C1. That known seat has a backrest with a number of pressure-actuable air chambers which are communicated with a control unit for controlling the pressure in the air chambers. The control unit is connected to an operating unit which is actuable by a user of the seat in order to adjust the contour or the lordosis of the backrest of the seat, as desired. With that known seat, the seat contour can be selectively curved forwardly in the upper, middle or lower portion of the lordosis region, by way of expansion of a respectively corresponding air chamber, as is described at column 4, lines 31 through 34.
DE 41 16 836 A1 describes a vehicle seat having a mechanical massage device and EP 0 270 699 B1 discloses a vehicle seat with air chambers for dynamic massage of the spinal column of a user of the seat, wherein the backrest is adapted to the S-shaped curvature of the spinal column of a user of the seat. This last-mentioned seat therefore also only takes account of lordosis.
Recent investigations however, on the basis of direct in-vivo intervertebral disc pressure measurements, show that the ideas which applied hitherto of sitting upright with a hollow back can no longer be sustained. In accordance with these most recent findings, sitting is no more stressful than standing, in which respect when sitting the pressure in the intervertebral discs in the seated posture with a round back (=kyphosis), which hitherto was frowned upon as being casual and lax, is even reduced to half. The comfortable seated posture with a slightly round back produces a markedly lower level of pressure loading than the upright posture with a rounded back (=lordosis) which was hitherto recommended by the back experts.
In consideration of those aspects the object of the present invention is to provide a seat of the kind set forth in the opening part of this specification, with which it is not only possible to adopt a hollow-back position but also a rounded-back position in order to correspondingly relieve the load on the intervertebral discs of the user of the seat.
In accordance with the invention, in a seat of the kind set forth in the opening part of this specification, that object is attained in that the backrest is displaceable between convex lordosis positions and concave kyphosis positions in dependence on the respective backrest inclination.
The configuration according to the invention of the seat with a backrest which is displaceable between convex lordosis positions and concave kyphosis positions in dependence on the respective inclination of the backrest affords the advantage that the spinal column of the respective user of the seat can be actively adapted to hollow-back and rounded-back positions. That provides for a changing pressure loading in respect of the intervertebral discs. As a consequence of that changing pressure loading, the advantage is enjoyed that the intervertebral disc is nourished as a consequence of its xe2x80x9csponge principlexe2x80x9d.
In the case of the seat according to the invention, it has proven to be desirable if the backrest in a steeply inclined setting is set curved convexly forwardly into an associated lordosis position and in a shallowly inclined position is set curved concavely rearwardly into an associated kyphosis position. That provides that the respective user of the seat assumes a hollow-back configuration in the corresponding upright position of the seat and a rounded-back configuration in a flatter position. It will be appreciated that it is also possible to provide for a kyphosis position in a steeply inclined position and a lordosis position in a flatly inclined position.
In the case of the seat according to the invention the seat squab can be stationary, that is to say non-adjustable. It is however also possible for the seat squab to be displaceable in the longitudinal direction of the seat and for the backrest to be displaceable in respect of its inclination and thus between lordosis and kyphosis settings, in dependence on the longitudinal seat squab setting. That provides an increase level of seat comfort, in comparison with a seat according to the invention with a seat squab which is not displaceable. In the case of a seat of the last-mentioned kind, it has proven to be advantageous if the backrest, in a set-back position of the seat squab, is set steeply inclined into a corresponding lordosis position and, in a set-forward position of the seat squab, the backrest is set in a shallowly inclined condition into a kyphosis position. That can take even better account of the anatomical aspects of seat users of different sizes.
Likewise it is possible for the seat squab to be displaceable in respect of its inclination and for the backrest to be displaceable in respect of its inclination and thus between lordosis and kyphosis positions, in dependence on the inclination of the seat squab. In a seat of the last-mentioned kind in a shallow position of inclination of the seat squab the backrest can be set in a steeply inclined condition into an associated lordosis position and in a forwardly upwardly inclined position it can be set in a shallowly inclined condition into an associated kyphosis position. This also makes it possible to take account of the anatomical factors of various users of the seat.
A still more improved seat with enhanced seat comfort is afforded if the seat squab is displaceable in the longitudinal direction of the seat and simultaneously in respect of its inclination and therewith the backrest is displaceable between corresponding lordosis and kyphosis positions.
In the case of the seat according to the invention the backrest can be displaceable statically between lordosis and kyphosis positions. As already stated above, that not only provides for an alternating pressure loading in the intervertebral disc, but it also provides for nutrition for the intervertebral disc as a consequence of its xe2x80x9csponge principlexe2x80x9d. It can be desirable if, in the seat according to the invention, the backrest is displaceable dynamically between lordosis and kyphosis positions in order not only to provide a desired pressure relief effect for the intervertebral disc as well as nutrition therefor, but also to provide a massage effect. All that has a correspondingly positive effect in terms of seat comfort.